1 Field of the Invention
The present invention relates to a method for preparing retro-reflective sheet with high abrasion resistance which is especially formed according to the following process: on the pattern releasing paper, the first coating layer one component PU resin mixed with reflective particles is coated initially; after drying, the second coating layer two component PU adhesive agent is coated; after being dried, a kind of paste is coated on it; finally, substrate is adhered. After drying and curing, pattern paper is divested from the resin, while solvent is used to solve part of the PU resin, leaving reflective particles exposed and hardened, forming final product. The material produced characterized in high abrasion resistance and using soft material as substrate. In accordance with the invention, the material is well suited to commercial uses like coat, vest, shoes, cap, poster, and the like.
2. Description of the Prior Art
Many patents have been disclosed for composition of retro-reflective material layer and the producing method thereof in U.S. Pat. Nos. 2,432,928, 2,440,584, 2,543,800, 2,397,702, 4,104,102, and the like, wherein retro-reflective plate containing one layer of glass beads is mentioned. Various retro-reflective layer invented in these U.S. Patents serve various commercial and industrial fields, such as mark of highway, traffic retro-reflective plate, and the like, which posses the property of reflecting the ray incident to the main part of the sign, and ray reflected will actually go along the original route, returning to source of the ray. Viewing from the aspect of applying the laminate structure of the retro-reflective plate, it""s important to have excellent optical transparence, which make the rays be reflected efficiently when rays entering into the laminate structure with a relative small angle. So a flexible layer structure will benefit the print and printing ink to deposit, and benefit each laminate to bond closely within the layer structure, presenting the feature of weather resistance and glass beads being fixed firmly on the laminate structure.
Most commercially available retro-reflective materials have good retro-reflective effect, but fail to be abrasion resistive, and glass beads contained in the retro-reflective materials frequently divest off after couple of rubbing. The reason is that before the substrate is hardened, the glass beads just spreads on the resin, being fixed on it physically. After hardening, the fixation is not so strong between the resin and the glass beads that the retro-reflective materials fail to be abrasion resistive. Additionally, hardened resin simply arranges in plain style, not perfect for retro-reflective performance. In present market, the retro-reflective material is limited to serving as highway mark, traffic retro-reflective plate and industrial safety sign for the reason that the substrate is made from hard material. Never see any retro-reflective materials suitable for any commercial fields like coat, vest, shoes, cap, poster made from soft substrate in the market.
For these reasons, after dedicating study and research, the invention presents a process as following: initially coating the first coating layer one component type polyurethane (PU) resin mixed with glass beads on the releasing paper with embossed grain; after drying, further coating the second coating layer two component type PU resin containing colorant, then drying it; above this layer, coating a kind of paste; finally, adhering the substrate; after pre-drying and curing, divesting releasing paper from the layer structure; finally, using solvent to solve the divested layer structure, leaving glass beads exposed and hardened, forming a retro-reflective material with glass beads being firmly fixed and characterized in abrasion resistance.
The following is a detailed description of the invention.
The primary technical characteristics of the invention is using the first coating layer one component type PU resin in appropriate weight as the matrix resin of the retro-reflective material. It""s necessary for the resin to apply a balance structure to exhibit excellent resistance to abrasion, heat adhesion and corrosion. The first coating layer should apply one component type PU having an excellent resistance to heat, to benefit subsequently drying and curing which are useful for heat-resistance. Generally, the key of increasing heat resistance of the PU resin is to enhance the cohesive strength, for example, to increase the content of hard segment.
Although PU resin with increased content of hard segment has fine heat-resistant performance, some problems still exits, for example, during processing of the releasing paper and the second coating two component type PU resin, especially when lamination process (referring to the process of coating the second layer on the first layer) is carried out in a short heating period and under incomplete drying, full heat-resistant performance has not be imparted to various layer.
To eliminate the history problem of not fully imparting heat-resistant performance, one object of present invention is to provide a kind of one component type PU resin as the first coating layer, instead of using cross-linking agent, therefore when lamination process is carried out under incomplete drying, one component type PU resin with heat-resistant performance can be obtained.
PU resin used in one component PU resin of present invention comprises polyol component, poly isocyanate component and organic solvent.
Examples of preferred polyol component are polyester polyol and polyether polyol. The former can be produced in addition reaction by reacting ethylene oxide and/or propylene oxide with small molecular weight polyol such as glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2 butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, hexamethylene glycol, hydrogenated bisphenol A, bisphenol A, trihydroxy methyl propane, glycerin or polyethylene glycol, polypropylene glycol, polyethylene/polypropylene glycol, poly caprolactone polyol, poly alkene polyol, polybutadiene polyol. The latter can be produced by reacting polyol with polybasic carboxylic acid. Suitable polybasic carboxylic acid can be aliphatic, alicyclic, aromatic or heterocyclic, preferably substituted by halogen atom and/or unsaturated polyester. Preferred polyester polyol includes glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 2-xcex2-hydroxybutylene glycol, 1,6-hexamethylene glycol, 1,7-heptamethylene glycol, 1,8-octylene glycol, 1,12-dodecane glycol, 1,18-octadecane glycol, neopentyl glycol, hexamethylene glycol, bis(1,4-hydroxy methyl) cyclohexane, 2,2-bis(4-hydroxy cyclohexyl) propane, 2,2-(bis-xcex2-hydroxy ethoxy) phenyl propane, 2-methyl-1,3-butyleneglycol,3-methyl-1,5-pentamethylene glycol, 2,2,4-trimethyl-1,6-hexamethylene glycol,2,4,4-trimethyl-1,6-hexamethylene glycol, glycerin, 1,1,1-trihydroxy methyl ethane, 1,2,6-hexane triol, 1,2,4-butatriol, tris-(p-hydroxyethyl) trimeric isocyanate, isoamyl tetra-alcohol, mannitol, sorbitol, diethylene glycol, dipropylene glycol, bibutylene glycol, xylyl glycol and hydroxy valeric neopentyl glycol ester. Abovementioned polybasic carboxylic acid can be succinellite, hexane diacid, 1,8-octanedioic acid, nonanedioic acid, decanedioic acid, phthalic acid, p-phthatic acid, m-phthatic acid, trimesic acid, pyromellitic acid, tetrahydric phthalic acid, hexahydric phthalic acid, hexahydric terephthatic acid, dichloro phthalic acid, tetrachloro phthalic acid, methylene bridge tetrahydric phthalic acid, dibasic fatty acid, pentanedioic acid, maleic acid, fumaric acid and anhydride thereof, dimethy p-phthatiate ester, p-phthatic acid bidiol ester. During preparation of polyester polyol, use any mixture of abovementioned polyol mixing with any mixture of abovementioned poly dicarboxylic acid and/or anhydride or ester thereof. Preferred ratio of polyester polyol with molecular weight from 1,000 to 5,000, preferably from 1,500 to 3,000, and polyether polyol with molecular weight from 1,000 to 5,000, preferably from 2,000 to 3,000 in all amount of polyol component is from 1/9 to 9/1 by weight, preferably from 3/7 to 7/3 which can produce coating material with excellent resistance to abrasion and heat. The abovementioned polyester polyol and polyether polyol may be used alone or in combinations of two or more. But the ratio of polyol in all amount of mono liquid PU resin is from 15% to 20% by weight.
Examples of preferred poly isocyanate component are poly aliphthalic isocyanate, alicyclic isocyanate and aromatic isocyanate. Preferred aromatic isocyanate comprises: tolylene diisocyanate (TDI), diphenyl methane diisocyanate (MDI), xylene diisocyanate (XDI), 3,3xe2x80x2-dimethoxy-4,4xe2x80x2-biphenyl diisocyanate, 1,5-naphthalene diisocyanate, 1,5-tetrahydronaphathalene diisocyanate, 2,4-methylene phenyl diisocyanate, 2,6-methylene phenyl diisocyanate, 4,4-diphenyl methane diisocyanate, 2,4-diphenyl methane diisocyanate, phenylene diisocyanate, xylenyl diisocyanate and tetramethyl xylenyl diisocyanate. Preferred acyclic isocyanate comprises: tetramethane diisocyanate (TMDI), hexylmethane diisocyanate (HMDI), cyclohexyl diisocyanate, 4,4-bicylcohexyl methane diisocyanate, 2,4-bihexyl methane diisocyanate. Preferred alicyclic isocyanate comprises isophorone diisocyanate (IPDI). Using diphenyl methane diisocyanate (MDI) and isophorone diisocyanate (IPDI) can induce coating layer with excellent resistance to abrasion and heat. The abovementioned poly isocyanate may be used alone or in combinations of two or more. The application amount of poly isocyanate to one component PU resin is from 5% to 10% by weight.
Examples of preferred organic solvent are acetone, methyl ethyl ketone, methyl benzene, xylene, dioxane, tetrahydro furan, N-methyl-2-pyrrolidone, dimethyl formaldehyde, dimethyl acetoaldehyde, dimethyl sulfoxide and ethyl acetate, preferably dimethyl formaldehyde, dimethyl acetoaldehyde and dimethyl sulfoxide. The ratio of organic solvent in total amount of one component type PU resin is from 70% to 80% by weight.
One component type PU resin used in present invention consists of PU resin produced by polyol reacting with poly isocyanate in organic solvent, solvent, reflective particles and additives. In order to make the interlayer structure comprising the first coating layer one component type PU resin, the releasing paper and the second coating layer two component type PU resin containing colorant, has heat-resistant performance, joint use of various additives in the formulation of the first coating layer one component PU resin is certainly permitted.
Preferred particle diameter of abovementioned reflective particles, example of glass beads is not less than 100 xcexcm, which is in favor of preventing from distortion of shaped product and enhance intensity and heat-resistance of first coating layer one component type PU resin. Surface of glass beads used violently reacts with commonly used silane type coupling agent and is well absorbed to the resin. Preferred particle diameter of the glass beads is in the range between 10 and 100 xcexcm. Considering the heat-resistant adhesive performance of the layer structure consisted by the first coating layer one component type PU resin and the second coating layer two component type PU resin, abrasion resistance performance of the retro-reflective material, and enhancement of reflection, the ratio of glass beads in total amount of the first layer one component type PU resin is from about 1:4 to about 4:1 by weight, preferably 3:1.
Examples of preferred additives are tackifying agent such as rosin latex, terpene latex, petroleum resin latex; filling agent such as graphite, clay, talcum powder, silicon dioxide, mica, calcium carbonate, aluminium hydroxide; additives such as silicon dioxide sol, alumina sol; film forming auxiliaries such as alkylene glycol; silane coupling agent; surfactant; levelling agent; antioxidant additive; antifoaming additive; viscosity reducing agent; plasticizers; pigment and dyestuff; flame retardant; lubricant, and the like.
Generally, even without crosslinking agent in the first coating layer one component PU resin presented by the invention, the first coating layer one component PU resin also has excellent heat-resistant performance. Only when other performance like weather resistance and moisture-heat resistance is needed to introduce, crosslinking agent. Preferred crosslinking agent includes epoxy resin, isocyanate, ethylene imine, carbodiimide, and the like.
In present invention, for the releasing paper, coated with the first coating layer one component type PU resin mixed with reflective particles, it can be made from PVC, PE, PP, cellulosic pulp or compound thereof. Surface style is preferably embossed grain or plane grain. There""s no specific limitation for the coating means of the first coating layer one component type PU resin, just usual method like knife coating, roll coating, bar coating, curtain coating, spray coating, squeez coating, and the like. Considering subsequent process and use of retro-reflective material, coating depth should be between 30 and 250 xcexcm, preferably 60 and 200 xcexcm. When necessary, coating can be carried out in one time or several times.
The first coating layer one component type PU resin mixed with reflective particles is dried. Temperature and time of drying are not particularly limited, just being set to vaporize the solvent included in the first coating layer one component type PU resin. Then the first coating layer one component type PU resin is dried to tack free, to benefit heat bonding of the second coating layer two component type PU resin containing colorant.
Furthermore, on the coated the first coating layer one component type PU resin, coating process of the second coating layer two component type PU resin containing colorant is carried out. Two component type PU resin used in the second coating layer two component type PU resin containing colorant, normally comprises polyol component and isocyanate component.
Polyol component presented in the second coating layer two component type PU resin in the invention, preferably comprises mixture of polyester polyol and polyether polyol, dominatingly neopentyl glycol. Polyol in the polyol component, is used to benefit an excellent adhesive strength and mechanical strength for the second coating layer two component type PU resin containing colorant and paste subsequently coated on it, wherein the amount of neopentyl glycol used to total polyol component is about from 40 to 80% by weight. In addition, the polyol component used here can still include the one applied in the first coating layer one component type PU resin. Combining this typical polyol component dominatingly consisted by neopentyl glycol with solvent mixture is helpful to the second coating layer two component type PU resin containing colorant and paste subsequently coated on it in the aspect of excellent bonding intensity and mechanical strength. Inclusion of vibration-to-influence resin and flowing additive is applicable. Solvent mixture used herein refers to ethyl acetate, butyl acetate, propylene glycol monomethyl ether ethyl ester, benzene or xylene, with any proportion in the mixture.
Preferred isocyanate component is mixture of prepolymer of poly isocyanate, typically including poly acyclic isocyanate, alicyclic isocyanate and aromatic isocyanate. Preferred aromatic isocyanate comprises toylene diisocyanate (TDI), diphenyl methane diisocyanate (MDI), xylene diisocyanate (XDI), 3,3xe2x80x2-dimethoxy-4,4xe2x80x2-biphenyl diisocyanate, 1,5-naphthalene diisocyanate, 1,5-tetrahydronaphathalene diisocyanate, 2,4-methylene phenyl diisocyanate, 2,6-methylene phenyl diisocyanate, 4,4xe2x80x2-diphenyl methane diisocyanate, 2,4xe2x80x2-diphenyl methane diisocyanate, phenylene diisocyanate, xylenyl diisocyanate and tetramethyl xylenyl diisocyanate. Preferred acyclic isocyanate comprises: tetramethane diisocyanate (TMDI), hexylmethane diisocyanate (HMDI), cyclohexyl diisocyanate, 4,4-bicylcohexyl methane diisocyanate, 2,4-bihexyl methane diisocyanate. Preferred alicyclic isocyanate comprises: isophorone diisocyanate (IPDI). Particularly preferred diphenyl methane diisocyanate (MDI) and isophorone diisocyanate (IPDI) induces coating layer with excellent wearproof and heat-resistant performance. Either use abovementioned three kinds of isocyanate separately or jointly. Preferably use solvent mixture together with the isocyanate componet. Just like above, solvent mixture used herein refers to ethyl acetate, butyl acetate, propylene glycol monomethyl ether ethyl ester, benzene or xylene, with any proportion in the mixture.
As to colorant used in the second coating layer two component type PU resin in the present invention, no specific limitation to it, just mixture of inorganic pigment, comprising natural mineral and synthetic pigment and organic pigment, comprising lake color and insoluble colorant. Color of the second coating layer two component type PU resin exhibits through reflection of reflective particles in transparent the first coating layer one component type PU resin.
Still, the coated the second coating layer two component type PU resin is dried to tack free. Like above, temperature and time of drying are not particularly limited, just being set to vaporize the solvent included in the second coating layer two component type PU resin. The second coating layer two component type PU resin is dried to tack free, for the convenience of heat bonding of subsequent paste on it.
Finally, substrate is glued by paste. After pre-drying and curing, releasing paper is divested. Solvent is used to solve the first coating layer one component type PU resin, leaving reflective particles exposed and hardened, to get a retro-reflective material characterized in abrasion performance. Used paste is normal adhesive used by substrate. Examples of preferred substrate in present invention are PVC, nylon, polyester, ABS, polyurethane, PE, PP, TPO (olefin substrate), cellulosic product, nature leather, synthetic product, Al (aluminum), Cu (copper), Fe (iron), stainless steel, paper, timber, MDF board, man-made board, glass. Preferably, paper, nature leather, cellulosic product and synthetic product are used in commercial fields like coat, vest, shoes, cap, poster. Substrate is glued on the paste. After pre-drying and curing, releasing paper is divested. Solvent is used to solve the first coating layer one component type PU resin, leaving reflective particles exposed and hardened, to get a retro-reflective material characterized in high abrasion resistance performance. Temperature range of drying and curing are not particularly limited, depending on the necessary of applied paste and the second coating layer two component type PU resin. Examples of preferred solvents used to solve the first coating layer one component type PU resin are acetone, methyl ethyl ketone, methyl benzene, xylene, dioxane, tetrahydro furan, N-methyl-2-pyrrolidone, dimethyl formaldehyde, dimethyl acetoaldehyde, dimethyl sulfoxide and ethyl acetate, preferably dimethyl formaldehyde, dimethyl acetoaldehyde and dimethyl sulfoxide. The abovementioned solvent may be used alone or in combinations of two or more.
Adding one or two layer of transparent membrane for print protection on the highly abrasion resistance retro-reflective material produced by above described process can enhance surface reflection effect and protect the surface. After carrying out the process of drying, curing and divesting of the releasing paper, roller with embossd grain can be used to roll and press the retro-reflective material so that surface grain pattern is exhibited. Finally hardening process is carried out.
Retro-reflective performance of the highly abrasion resistance retro-reflective material produced by above described process is tested according to Test Method for Retro-reflective Plate and Retro-reflective Tape stipulated in Item 3.2 of Retro-reflective Performance Test Method in CNS 4346. Abrasion resistance performance of that is tested according to the Taber Method stipulated in ASTM D3884 on a Taber abrasion test machine (Model 5130, made by US Taber Industries Company). During test, put on 1 kg of load on the retro-reflective material produced in the present invention, then rotate it with a 150 mesh H22 grinding wheel by 1000 rotation. After that, the tested material is assessed.
Process of the present invention will be described below in detail by referring examples. However, the present invention is not limited to the thereto.